For many centuries spiral stairs have been a fascination for architects, designers, builders and owners. Even more fascination occurred when the spiral design encompassed single supports either on the exterior wall or on an interior column. As strength of materials improved, construction designs provided for supports at the base and the floor above. The greater the ceiling height the more complex and spectacular the designs became.
Compared with elevators, straight-line escalators serving one floor at a time in both directions became an improvement in rider movement where less than a dozen floors were involved.
Next came the transition from straight to curved and even spiral escalators. The preference for spiral escalators became popular since the design requires less horizontal space than straight escalators, especially where there are variations of ceiling height. A spiral escalator was constructed at London's Holloway Road underground station in 1906 only to be dismantled almost immediately. The Mitsubishi Electric Corporation has successfully developed commercial designs and has manufactured curved and spiral escalators since the 1980s.
All of the current designs are limited to serve only one pair of floors at a time. Separate escalators are required for ascending or descending installations and are usually constructed side by side, requiring a large horizontal space. Only half of the steps are in use at any time for all escalators, due to the continuous travel requiring the returning steps passing under the conveyor. This results in having steps in use only half of the time.
Ever since 1883 when the first escalator (called “inclined elevator”) was invented, the escalator has been a favorite means for mass transportation of riders in preference to vertical elevators. Through the years many inventions have been processed that attempted to improve the straight line escalators by: making more efficient use of the horizontal space required, serving multiple floors without requiring the riders to leave and re-enter at each floor, using all steps all of the time, utilizing large vertical space, improving the aesthetics and architecture, and increasing rider movement more economically and efficiently.
This invention achieves all of these aspirations by providing a circular tower spiral escalator structure with counter-rotating sprocket wheels that use a chain to connect and drive the ascending and descending escalator steps. Also, this invention provides at the top and bottom floors, robotic transfer of the escalator steps between the sets of ascending and descending steps. This eliminates the necessity for the upside down empty return of the steps underneath those steps that are bearing a load. For a given installation, this reduces the total number of steps, tracks and chains by about half.